Is it a matter of size? I was under the impression that a parry was more gaining control of the opponents swing to send it off course and less of a weapon block. I know if I can strike my enemies weapon with a great sword I will send it off course, but isn't it also much harder to control the great sword to do that with in the first place? Medium weapons like long swords and such seem like the best parry weapons while the others all have different benefits and drawbacks. A dagger limits the momentum of your swing but it's very easy to turn and position to deflect an incoming attack. Larger weapons offer more force to counter with but are harder to adjust if needed.
I do like the concept overall and look forward to further developments.